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46 lines
1.3 KiB
Markdown
46 lines
1.3 KiB
Markdown
Extracted from [nim-libp2p](https://github.com/vacp2p/nim-libp2p/blob/cfd631457ae865852d17ed77a9d4d3ea37710082/libp2p/crypto/crypto.nim#L161) (`libp2p/crypto/crypto.nim`) and `codex/rng.nim` in [nim-codex](https://github.com/codex-storage/nim-codex) so that it does not depend on libp2p anymore:
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```nim
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{.push raises: [].}
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import bearssl/[rand, hash]
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proc newRng*(): ref HmacDrbgContext =
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# You should only create one instance of the RNG per application / library
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# Ref is used so that it can be shared between components
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# TODO consider moving to bearssl
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var seeder = prngSeederSystem(nil)
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if seeder == nil:
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return nil
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var rng = (ref HmacDrbgContext)()
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hmacDrbgInit(rng[], addr sha256Vtable, nil, 0)
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if seeder(addr rng.vtable) == 0:
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return nil
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rng
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type
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RngSampleError = object of CatchableError
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Rng* = ref HmacDrbgContext
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var rng {.threadvar.}: Rng
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proc instance*(t: type Rng): Rng =
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if rng.isNil:
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rng = newRng()
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rng
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# Random helpers: similar as in stdlib, but with HmacDrbgContext rng
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# TODO: Move these somewhere else?
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const randMax = 18_446_744_073_709_551_615'u64
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proc rand*(rng: Rng, max: Natural): int =
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if max == 0:
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return 0
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while true:
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let x = rng[].generate(uint64)
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if x < randMax - (randMax mod (uint64(max) + 1'u64)): # against modulo bias
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return int(x mod (uint64(max) + 1'u64))
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```
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